A conventional active noise control apparatus detects noise which is a control target by using a detecting means such as a microphone or various types of sensors, and outputs a control sound having the same amplitude and the inverted phase to cancel out the noise, thereby silencing the noise.
In the present invention, vibration or noise which machinery generates is collectively referred to as noise.
Further, some of conventional active noise control apparatuses include an error microphone placed at a desired position, and perform a control to keep the silencing effect to be maximum by correcting the control sound on the basis of a signal from the error microphone. At this time, when disturbance unrelated to noise is collected by the error microphone, the active noise control apparatus operates in such a way as to silence the sound including the disturbance. As a result, the effect of silencing the originally targeted noise may be lost temporarily, or the control sound may become abnormal noise. As examples of such disturbance, for example, there are a blowing sound which is caused by wind hitting the error microphone, a strike sound which is caused by a person or an object touching the error microphone, and so on.
To solve this problem, for example, Patent Literature 1 discloses a method of avoiding an occurrence of abnormal noise by reducing a control sound using a muting process. Further, Patent Literature 2 discloses a method of, in an active noise control apparatus that adjusts a control sound by using an adaptive notch filter, stabilizing a silencing effect by adjusting a step size which is a parameter for controlling an amount of updating of a filter coefficient.